Oil and gas wells produce oil, gas and/or byproducts from underground reservoirs. Oil and gas reservoirs are formations of rock containing oil and/or gas. The type and properties of the rock may vary by reservoir and also within reservoirs. For example, the porosity and permeability of a reservoir rock may vary from reservoir to reservoir and from well to well in a reservoir. The porosity is the percentage of core volume, or void space, within the reservoir rock that can contain fluids. The permeability is a measure of the reservoir rock's ability to flow or transmit fluids.
Capillary pressure refers to a difference in pressure across a fluid interface in a capillary. Capillary pressures in a reservoir generally depend on the porosity and permeability of the rock as well as other properties of the rock and the fluids. Unconventional reservoirs, which may include shale reservoirs, tight gas reservoirs, and other types of low permeability reservoirs, typically exhibit high capillary pressures. High capillary pressures in a reservoir may lead to phase trapping rendering that phase immobile in the reservoir, which may inhibit or hinder production of resources.
Oil and gas production from a well may be stimulated by fracture, acid or other production enhancement treatments. In a fracture treatment, fluids are pumped downhole under high pressure to hydraulically fracture the reservoir rock in order to connect a larger portion of the reservoir to the wellbore. In some implementations, fracture fluids without proppants are injected into the formation to fracture the formation, and fracturing fluid with proppants are then pumped into the formation to hold the fractures open.